Work is continuing on the possible role of hepatic "futile" substrate cycles to regulate carbon flow to and from glucose. Tracer methods using reversible (C14) and irreversible tracers (H3) of glucose are being developed for this purpose and the role of such hormones as glucagon, insulin and epinephrine are being examined. Experiments will be carried out in rats, rabbits and marine fish. Fish are currently being used since the slower metabolic rate and slower hormonal responses may allow a closer look at the initial hormonal events which occur too rapidly in mammals to detect. Work will also be renewed on the role of adrenal steroids in the regulation of the glycogen phosphorylase cascade, and on enzymatic mechanisms involved in growth hormones control of metabolism.